Digital television, popularly referred to as DTV, is an enhanced television system capable of transmitting and receiving digitized signals, displaying digital images and playing digital audio. While some of these features may be present in current analog television systems such as national television standards committee (NTSC), sequential couleur avec memoire (SECAM) and phase alternate line (PAL), the combination of digitized transmission, reception, video and audio distinguishes digital television from current analog television systems.
Digital television employs various digital signal processing techniques and utilizes scarce bandwidth in a more spectrally efficient manner to transport and present audio and video signals in a way that is superior to current analog television systems. In this regard, digital television allows more channels containing more information to be broadcasted within an equivalent bandwidth utilized by current analog television systems. Accordingly, any excess bandwidth can be re-allocated for use by other types of communication systems. Broadcasters utilizing digital television systems are therefore, capable of providing over-the-air television signals containing higher picture resolutions than current analog broadcast television systems. Broadcasters utilizing digital television systems may also have the capability to provide multicasting and datacasting services using the same bandwidth allocated for conventional analog television systems. For these reasons, Congress mandated that current broadcast television service must, in time, be completely converted to digital television.
While digital television (DTV) utilizes the same broadcast very high frequency (VHF) spectral band and ultra-high frequency spectral (UHF) band as conventional television broadcasting systems, digital television utilizes different modulation techniques than conventional analog television broadcasting systems. Conventional analog television broadcasting systems modulate video using amplitude modulation (AM) and the accompanying audio is modulated using frequency modulation (FM). DTV utilizes a plurality of modulation techniques for transmitting and receiving packetized digital signals. In the United States of America, an eight level vestigial sideband (VSB) modulation scheme is utilized. In some regions of Europe and Asia, for example, coded orthogonal frequency division multiplexing is the modulation scheme of choice. On the other hand, digital satellite systems (DSS) utilize quadrature phase shift keying, while cable television (CATV) system utilizes quadrature amplitude modulation (QAM).
In the United States, a plurality of broadcast formats promulgated by the Advanced Television Standards Committee (ATSC) has been adopted for DTV applications. Some of these formats comprise progressive-scan video comprising 480 scan lines referred to as 480p, interlaced 4:3 video having 480 scan lines referred to as 480i, interlaced video having 1080 scan lines referred to as 1080i and progressive-scan video having 720 scan lines referred to as 720p. Standard definition (SD) television (SDTV) utilizes the interlaced 480i and progressive 480p formats. The picture quality provided by SDTV is comparable in certain respects to conventional NTSC 525 lines systems. High definition (HD) television (HDTV) utilizes the interlaced 1080i and progressive 720p formats in a 16:9 aspect ratio. The resolution of the HDTV interlaced 1080i and progressive 720p formats may be converted to lower resolution such as the interlaced 480i and progressive 480p formats provided by SDTV.
In the US for example, DTV signals are modulated on an RF carrier using 8-level VSB or 8VSB, and transmitted in a six (6) MHz channel as compressed 4:2:0 MPEG-2 formatted packetized streams. These packetized streams contain both audio and video information. For this reason, a conventional analog system is unable to receive a transmitted DTV signal. In order to decode a received 8-level VSB signal, an ATSC-compliant DTV receiver or a set-top box is required.
FIG. 1 is a block diagram of a conventional digital television (DTV) receiver. Referring to FIG. 1, the receiver 100 comprises an antenna 102, a tuner 104, a demodulator block 106, an equalizer 110, a phase tracking block 112, a trellis decoder 114, a de-interleaver 116, a Reed Solomon (RS) decoder 118 and a de-randomization block 120.
The antenna 102 is coupled to the tuner 104, which is adapted to receive 6 MHz VHF or UHF signals. The tuner 104 includes a band pass filter that passes signals in the range of about 50 MHz to about 810 MHz, thereby rejecting any unwanted signals. The demodulator block 106 is adapted to receive and process NTSC signals and may include circuitry that is utilized to mitigate the effects of co-channel interference. The equalizer 110 is adapted to compensate for linear distortions that may have occurred during transmissions. The phase tracking block 112 may be utilized to track and eliminate unwanted noise. The trellis decoder 114 reduces co-channel interference and impulse noise. The de-interleaver 116 and the Reed Solomon (RS) decoder 118 may cleanup the signal and remove any unwanted burst interference that may affect image quality. The trellis decoder 114, de-interleaver 116 and the Reed Solomon decoder 118 significantly reduces errors that may occur in the received signal. The de-randomization block 120 is configured to receive the error corrected signal from the Reed Solomon decoder 118 and de-randomizes the error corrected signal using the same pseudorandom sequence utilized to randomize the original signal during transmission.
The receiver of FIG. 1 is adapted to receive and demodulate only 8-level VSB modulated signals. In most instances, the tuner 104, filter block 106, equalizer 110, phase tracking block 112, trellis decoder 114, de-interleaver 116, Reed Solomon (RS) decoder 118 and de-randomization block 120 are integrated into a plurality of integrated circuits (ICs) which have to be coupled together by suitable circuitry and/or logic. Accordingly, any receiver implementation utilizing these integrated circuits would require a significant investment in scare and expensive printed circuit board (PCB) real estate and complex design layouts. Even in instances where most of the components of FIG. 1 are integrated in a few integrated circuits, the resulting receiver is limited to North American digital terrestrial broadcast television signals. Furthermore, with the promulgation of standards such as the CableCard specification, any out-of-band signal processing would require additional ICs and/or circuitry to handle out-of-band signal processing. This would further require the use of additional PCB real estate, further increasing cost and design complexity.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.